Construct a new directory comparison object, to compare the
directories a and b. ignore is a list of names to
ignore, and defaults to ['RCS', 'CVS', 'tags']. hide is a
list of names to hide, and defaults to [os.curdir, os.pardir].
Print a comparison between a and b and common
subdirctories (recursively).
The dircmp offers a number of interesting attributes that may
be used to get various bits of information about the directory trees
being compared.
Note that via __getattr__() hooks, all attributes are
computed lazilly, so there is no speed penalty if only those
attributes which are lightweight to compute are used.